Thermochromic display system



Aug. 6, 196s G. E. KEITH, JR 3,396,378

` THERMOCHROMIC DISPLAY SYSTEM Filed Aug. 17, 1965 5 Sheets-Sheet l Aug. 6, 1968 G. E. KEITH, JR 3,396,378

THERMOCHROMIC DI SPLAY SYSTEM Filed Aug. 17, 1965. 5 Sheets-Sheet 2 Aug. 6, 1968 G.E.KE|TH, JR

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THERMOCHROMIC DI SFLAY SYSTEM Filed Aug. 17, 1965 5 Sheets-Sheet 4 177,? 7 /mf/ far/Mw) 5 L M ,f

G. E. KEITH, .JR 3,396,378

THERMOCHROMIC DISPLAY SYSTEM 5 Sheets-Sheet 5 Aug. 6, 1968 Filed Aug, 17, l1965 United States Patent 3,396,378 THERMOCHROMC DISPLAY SYSTEM George E. Keith, Jr., Del Mar, Calif., assigner to General Precision Systems luc., a corporation of Delaware Filed Aug. 17, 1965, Ser. No. 480,327 Claims. (Cl. 340-324) ABSTRACT 0F THE DISCLGSURE A thermochromic panel having a multiplicity of character displays each of which comprises a plurality of separately energizable bars is coupled through logic control circuitry to 'an associated computer. During each write cycle, information derived from the computer is stored in a circulating register which is adapted to shift one bit time to the right upon each circulation. Since each character code comprises four bit times, new character code information may be unloaded into a four-stage static display register every four circulations. The display register is then coupled through suitable control logic to a preselected character display for energizing the bars thereof in accordance with the code stored in the static display register.

The present invention relates to an improved display system for use, for example, with a digital computer; and it relates more particularly to an improved display system which utilizes thermochromic substances to produce the display.

The display of the present invention may be used, for example, in conjunction with an airborne navigational general purpose computer, and an embodiment of the invention will be described in the ensuing speciiication in conjunction with the control panel of such a computer.

It will |become evident as the description proceeds, however, that the thermochromic display of the invention may be used in a wide variety of applications both airborne and non-airborne, and both military and nonmilitary.

The display of the invention may replace, for example, present day data display systems using electrically energized indicating lamps, and the like, to form characters corresponding to output data derived from the associated computer.

The use of a thermochromic display is advantageous in that it is easy to read even under high ambient light levels, and in that it comprises a rugged and sturdy solid state unit. Moreover, a thermochromic display is not susceptible to burn out so that replacement requirements are minimized and general maintenance is virtually eliminated.

T hermochromic display units rely on the fact that certain substances change color as a function of their temperature. For example, chemicals such as the double iodide of mercury Aand silver (Hgl2-2Agi), or the double iodine of mercury and copper (HgI2.2CuI) may be utilized in such a display. Typical of the color shifts exhibited by such chemicals is a shift from yellow (5,000 A.) to red (6,500 A.), as the temperature is increased beyond a particular threshold. In the case of the first mentioned chemical, this temperature threshold is around 50 C.

A principal object of the present invention, therefore, is to provide an improved display system using a thermochromic substance, and one which is thoroughly reliable in its oper-ation, which is relatively simple and inexpensive in its construction, and which is capable of a long operational life with little or no maintenance requirements.

In the drawings:

FIGURE 1 is a schematic representation of a control panel of a computer incorporating a thermochromic dis- 3,396,378 Patented Aug. 6, 1968 HCC play which is controlled by the improved system of the present invention;

FIGURE 2 is a sectional representation of thermochromic display panel;

FIGURE 3 is a plan view of a thermochromic display panel, which includes a segmented display so that different numerals, for example, may be represented;

FIGURE 4 is a group of schematic representations of different segment combinations which may be used in the display of the invention so that various numeral and letter characters may be formed;

FIGURE 5 is a table representing the character code used in the display system to be described;

FIGURE 6 is a fragmentary circuit representation of an appropriate drive system for the display system;

FIGURE 7 shows the control word format used in the control system associated with the display;

FIGURE 8 is a block representation of the aforesaid control system (as employing one embodiment of the invention; and

FIGURE 9 is a table showing the keyboard character loading times.

A computer control panel 10 for a navigational type of general purpose computer is shown in FIGURE 1. The panel includes a thermochromic display panel 12, which is controlled by the system of the present invention.

The thermochrornic display panel 12 is located at the upper left hand portion of the control panel, as shown in FIGURE 1. The two upper lines of the display panel 12 may be used, for example, to indicate latitude and longitude, respectively. In the illustrated example, the displayed latitude is 67 13.5 N, and the displayed longitude 169 27.6 W.

The two lower lines of the display 12 may be used to indicate such other data as, for example, bearing/range (BRG/RNG); ground track (G.T.); wind; and cross track/ along track (CT/AT).

The control panel 12 includes, for example, a decimal point display a, twenty-one numerical displays d-x; a N-S letter display aa; an E-W letter display bb, a a B,R,L,T letter display cc; and an A,R,S letter dd. The other symbol indications on the display panel 12 are permanently inscribed.

In the system to be described, longitude and latitude are displayed at all times, except when new values for these quantities are being entered. The remaining data is displayed when a read button 14 is depressed, and the desired type of data is selected by pushing the corresponding ones of a group of buttons 16, 18, 20 and 22.

The origin and destination data is entered into the computer by adjusting a pair of thumb switches 28 and 30 on the lower left hand corner of the control panel (l0. The computer mode is selected by the mode switch 32 at the lower right hand corner of the panel 10. The mode settings of the switch 32 may be, for example, stand-by, dead reckoning DR; dead reckoning/tacan iix DR/ TF; Flix l. Fix 2, and Oiif Inform-ation may be entered into the logic circuitry controlling display panel 12 by depressing button 15 if latitude and longitude data is being entered, or by depressing enter button 34 and one of the buttons 16, 18, 20 and Z2 corresponding to the data to be entered. The data is entered, as will be described, from. the input/output system of the computer, or through a keyboard 35. The data is displayed by the display panel i2 as it is being entered. The data is then stored in the computer when the store button 36 is depressed.

When longitude-latitude information is being entered into the control system -by way of the keyboard 35, the selection of North or South, East or West is made by the two switches 38 and 40 on the keyboard.

assasrs When the other data is being entered by means of lthe keyboard 35, the decimal point position for the lower line of the display 12 is selected by a switch 42. When data is being displayed by the computer, the computer selects the decimal point position, and the computer also selects the letters preceding the quantities being displayed.

When the read button 14 is depressed, the computer determines the quantities to be displayed by examining the setting of the mode switch 32, the settings of the origin and destination switches 23 and 30, and the settings of the data selection buttons.

The thermochromic display 12 comprises a panel coated with a thermochromic material, such as those mentioned above, which changes color when its temperature is raised above a particular threshold.

The temperature of the display panel 12 may be controlled in a localized manner by selectively passing electric currents through resistive wires which are imbedded in the panel. Different characters are displayed, as will be described, by using a plurality of wires, each energized independently and each generating part of the particular character.

The thermochromic display panel 12 may be constructed in a variety of ways. For example, as shown in FIGURE 2, a transparent substrate may be provided, and a surface of the substrate may be coated with a coating 52 of the selected thermochromic material. The transparent substrate may be composed, for example, of glass, or of any other appropriate transparent substance.

The heater elements 54, in the form, for example, of

resistive bars may be positioned on the coating S2 in selected patterns so that the different characters of the display 12 of FIGURE 1 may be formed. A protective coating 56 may be deposited over the resistive bars to form a rigid and effectively encapsulated unit.

Separate electric connections are made to each of the resistive bars S4, so that each may be independently energized. A typical arrangement, for example, for forming the numerical characters is shown in FIGURE 3. In the representation `of FIGURE 3, the resistive bars 5'4 are positioned in a selected grouping so that selective energization of the bars will result in the formation of the different numerical characters. A pair of electric leads extends to the respective ends of each bar; and each bar is separated and insulated from the others, so that the bars can be independently and selectively energized.

Thermochromic displays, as explained above, rely on the fact that certain substances change color as a result of their temperature. For example, the double iodide of silver and mercury thermochromic substance mentioned above will shift in color from yellow to red, as its temperature is increased above a temperature of about 50 C., and it will return to yellow when the temperature is decreased below that temperature.

The manner in which the different characters of the display 12 may be formed is shown in the schematic representations of FIGURE 4. It will be understood that the different bars shown in FIGURE 4 correspond to the resistive bar heater elements 54 discussed above.

The various parts of the character bars for the different displays are numbered 1 7 in FIGURE 4. The bars which are used to form the Various numerical characters in the numerical displays are shown, for example, in FIG- URE 4a. The `bars which are used to form` the different letter characters in the various letter displays are shown, for example, in FIGURES ib-4e. In the case of the letter characters, a bar may have several segments, and these segments appear in different displays. In the case of the decimal point display, the bar segments are in the form of dots The table of FIGURE 5 shows the smanner in which the different bars are selected in the diferent characters. This table also shows a four bit binary code which is used to select the lvarious characters. It will be observed that cartain of the bars in the different character displays bear the salme numbers. This means that these are all segments of one character ball The purpose is to extend the selection capabilities of the four bit binary code. Whenever that number appears from the character selecting logic, all the bar segments bearing that number are selected. I-Iowever, additional circuitry, as will be described, is used so that the selection of only one character display is made at any particular time.

The display drive circuitry is shown in FIGURE 6. As will be described, control logic is provided which selects the particular display to be activated at any particular time. At that time, the bar select logic, to be described in conjunction with FIGURE 8, responds to the character code established for the selected display to generate the corresponding bar selection signals. These signals are applied to the appropriate ones of the seven input terminals of the various displays, but activate only the display selected at that time by the control logic.

It will be appreciated that signals from the bar select logic are applied through a circuit, which includes the transistors lil-lli, to the seven left hand terminals of each display. These terminals in turn are respectively connected to one end of the various bars in the display. The other ends of the bars of each display are connected to the respective right hand terminals, these being connected together and to respective circuits, including the transistors 102, the latter circuits responding to the display selection signals from the control logic.

No provision is made in the particular embodiment under consideration for erasing characters. Erasure is provided in the embodiment by normal cooling. It wil1=be appreciated, of course, that artificial cooling could be used in order to speed up the erasure of the different characters from the display 12.

When a character is to be changed, a new character is written into the display and the previous character disappears as the corresponding portion of the thermochromic material cools orf. Furthermore, due to thermal delay, it is not necessary to energize the lbars of the ditte-rent displays continuously. Rather, each character may be written periodically, but rapidly enough so that the display itself gives a continuous reading. Thus the different characters may `be written in sequence in the different displays.

The word format used in the control system for the different characters of the display panel 12 of FIGURE 1 is shown in FIGURE 7. The illustrated words in FIGURE 7 each contain twenty-eight bits, with the most significant bit being at the left. Each of the illustrated characters of each word is made up of four binary bits, in accordance with the code table of FIGURE 5, and each controls a different display of the display panel 12 of FIGURE 1.

The control logic for the display system is shown in block -form in FIGURE 8. It includes four twenty-seven bit delay line registers, designated respectively 200, 202, 204 and 206; and four flip-Flops D1, D2, D3 and D4. The aforesaid registers and flip-iiops are interconnected to form a recirculating display register which holds all the data being displayed. The recirculating display register recirculates every four Word times, and 112 recirculations (448 word times) constitute a write cycle. Each character is written for 16 word times (465 a sec.) during each write cycle -of 448 word times (13.1 m. sec.). This allows twentyeight characters to lbe Written on the display 12, however, two of the characters are spares as shown in FIGURE 7 and are not used.

The data circulating in the control system comprises the four words shown in FIGURE 7, and these words circulate in the circulating register from the least significant bit of the word (A), that is, of the decimal point character; to the most significant bit of :the word (D), that is, of the North or South character. The characters are also Written on the display 12 in that order.

In order to simplify the selection of characters from the recirculating display register, the register is caused to shift right by one bit for each recirculation (four word times),

except the first circulation, during each write cycle (448 word times).

This right shift of the circulating display register is achieved by loading the circulating register from the llipflop D2 instead of from the ilipdiop D1, during the last 444 word times of the cycle. This results in the bit in the flip-flop D1 being lost `for the first character. However, since that particular bit is the least significant bit of the decimal point character, it is known Ito be a 1, as shown in the table of FIGURE 5. Therefore, this bit can be replaced whenever necessary.

The 448 word times of the write cycle are provided by a 64-sta'te binary word counter (made up of the ip-ops W1-W6) in the input/ output section of the computer, and by a 7-state counter made up of additional flip-flops W7- W9.

The aforesaid circulating re-g ister may be loaded from the input/ output track on the lmain memory of the computer, through an input/ output read amplifier (not shown) and by way of the select llogic 208 of FIGURE 8. Alternatively, information can be entered into the circulating register from the keybooard 35 of FIGURE 1, through a register K and also by way of the select logic 208.

The data in the circulating register is displayed on the display 12 of FIGURE 1 at all times. Every sixteen Word times (four recirculations), that is, word times 0, 16, 32 432, four bits (one character) are shifted out of the flip-flop D2 into the four ip-ilops S1, S2, S3 and S4 which make up an S register. These 'bits are decoded in the bar select logic 210 to control the selected display, as discussed in conjunction with FIGURE 6.

At the same time, the word counter W1W9, by way of the control logic 212, selects the corresponding display of the display panel 12 of FIGURE 1, which is to be activated at that particular time. The selected character is written f-or sixteen word times (four recirculations) while the recirculating display register shifts to bring the next character into position to be shifted in the S register.

A new character is Written every sixteen word times (except for the two blanks) until all the characters have been written into the system. The cycle then repeats. During the word time 0, when the decimal point is being written, only three ibits are shifted into the S register out of the flip-flop D2 because the least significant bit (in the flip-flop D1) was lost. The flip-flop S1 is then set to provide :the proper code.

The recirculating display register can be loaded from the input/ output track of the -main computer memory during the rst four word times W0-W3. Whether or not such loading is to take place is controlled by the push buttons on the control panel 10, as described in conjunction with FIGURE 1.

For example, if the read button 14 and one of the selection buttons 16, 18, 20 or 22 are depressed, data iS read from the input/ output track of the computer memory into the circulating display register during word times WTO to WT1. The data will be displayed, as explained, in the llower into lines of the display panel 12.

Then, during word times WTZ and WTS, longitude and latitude data is read from the input/output track of the `computer memory into the circulating register unless the lat/long button 15 is depressed. The latitude and longitude data, as explained above, is displayed on the upper two lines of the display panel 12.

As lan alternative, data can be loaded into the recirculating display register from the keyboard 35. This is achieved by depressing button 15 if latitude and longitude data is being entered or by depressing enter button 34 and one of the selection buttons 16, 18, ,and 22 corresponding to the data being entered.

If latitude and longitude data is selected by depressing the button 15, t-he data entered from the keyboard 35 will -be displayed on the upper two lines of the display panel 12.. On the other hand, if any one of the remaining buttons 16, 18, 20 or 22 is depressed, the data being entered from the keyboard 35 will be displayed on the lower Itwo lines of the display panel 12. Data is entered into the recirculating display register under the control of a character counter CC which is made up of four iiip-iiops CC1, CC2, `CC?, and CC4; and of a control counter KC which is made up of three flip-flops KCI, KC2 and KCS.

The character counter CC identifies the location in the circulating display register of the various characters, and thus indicates the position in the display where any particular character is to be placed. The table of FIGURE 9 shows the relationship between the different characters in the recirculating display register and the successive counts of the character counter CC. The table of FIGURE 9 also shows the word times during which the dierent characters are loaded into the circulating display register. Loading always occurs during the bit times FZ7-P24, that is, during the first four bit times of each word time indicated in the table of FIGURE 9. The bit times are derived from the computer and they are identified as FZ7-P0 for each word.

When the lat/long button 15 is depressed, the character counter CC is set in the zero state, and the upper two lines of the display panel 12 are cleared. Alternately, the lower two lines of the display panel 12 are cleared if the enter button 34 of FIGURE 1 is depressed. Clearing is accomplished by inserting the character code 1111, corresponding to a blank character, in the recirculating display register.

Characters are then entered from the keyboard 35 in the order shown by the table of FIGURE 9. The letters and the decimal point are entered automatically at the appropriate character times from the panel switches.

When a keyboard character button is depressed, the corresponding character code is entered into the K register Which is made up of four flip-flops lil-K4. The code is held in the K register until the proper word time is reached for the information to be fed through the select logic 208 into the circulating display register. Then, during the rst four bit times of the corresponding word time, as `set out in the table of FIGURE 9, the character code in the K register is shifted through the select logic 208 into the recirculating display register. The character counter is then incremented to the next character, and the circuit is ready for the next input from the keyboard 3S.

It may be noted that data which has been entered into the recirculating display register can be stored on the input/output track of the computer memory. This is achieved by depressing the store button 36 of FIGURE l. The flip-flops ST1 and ST2 control the store operation in conjunction with appropriate gating logic 216 in FIG- URE 8.

When the store button 36 is depresse-d, the system waits until Word time WT2 if a latitude or longitude operation is involved, as selected by the button 15; or the system waits until word time WTO if one of the other operations, as selected by one of the buttons 16, 18, 20 or 22 is involved.

The data from the recirculating display register is read from the flip-flop D1 into the input/output track of the computer memory for two word times through the gating logic 216 and through the input/output memory track write amplifier. After the computer has accepted the data, it turns on the store lamp 37 on the panel 10 in FIG- URE 1. The lamp remains on until the store button 36 is released.

It will be appreciated that the binary coded signals representing each character of the four words of FIGURE 7 are shifted into the S register and remain in that register a time suicient to permit the energized bars of the corresponding selected display to 'be heated to the aforesaid colorshift threshold temperature.

Then the binary coded signals in the S register are replaced by those representing the next character. This continues throughout the write cycle until all the displays have been activated. Then the write cycle is repeated, this repetition being sufficiently rapid so that the displays do 7 not have time to cool down below the threshold temperature, so that a continuous display is achieved due to the aforesaid thermal delay.

As mentioned above, in order to simplify the selection of characters in the recirculating display register, the register shifts right one bit for each recirculation. This is achieved by loading the recirculating display register from the flip-flop D2, instead of from the ip-op D1, for all recirculations except the first. For the rst recirculation, and in order to keep the recirculating display register in step with the word counter, the recirculation is from the flip-flop D1 and the reciroulating display register is loaded from that llip-op.

The following logic equations represent the logic circuitry involved in the various components of the display system shown in block form in FIGURE 8.

The invention provides, therefore, an improved control system for controlling the energization of a thermochromic type of display. The system of the invention is advantageous in that it provides a control of a thermochromic display panel in such a manner that a plurality of separate displays can be activated and controlled.

As described above, the activation of the displays is such that each is energized for predetermined intervals with the information to be displayed, so that due to thermal delay, a continuous display is achieved. At the same time, all the separate displays are activated in a sequential manner so that a continuous updating can be achieved throughout the plurality of displays on the panel.

The control system of the invention is also advantageous in that it permits a multiplicity of displays to be controlled by a limited binary code, the number of displays so controlled being beyond the normal capabilities of the code. This is achieved, as explained, by providing different segments of controlled bars throughout different displays, and sequentially selecting the displays in the manner described.

APPENDX "D Register (Flip-flops D1-D.t)

d1=D2 (set) Z= (reset) d2=D3 d4=MOS REG. OUTPUT 2=ms`m MOS is portion of display register made up by registers 200, 202, 204, 206 (FIGURE 8).

Cil

[CC' 'OJFCCTGJF (Ut/'1112) (summum (LA T/LONG) (CCT0+CCT6) (PBl-tPBs) (CCTs) -I- (CCT12) (ENTER).

DP Setting of decimal point switch 42 CHl-CHO Keyboard buttons 1-0 PB Push button switches 16, 18, 2t) and 22 N-S Switch 38 E-W Switch 40 What is claimed is:

1. A display system for use with a multi-unit thermochromic display panel, and the like, each unit of said display panel including a plurality of energizing bars for causing such unit to generate different characters, said display system including: control logic circuitry for selecting the different units of the display panel respectively in a preferred sequential order thereby defining a display cycle, bar select logic circuitry for selecting predetermined bars in each respective unit selected by said control logic circuitry during said display cycle, register means for recirculating at least one multi-character word during said display cycle, circuit means coupled to said circulating register means for introducing said multicharacter word therein, and means coupled to said circulating register trneans for serially deriving the individual characters of said multi-character word from said circulating register means in `synchronism with the selection of said different display units in said preferred sequential order, said lbar select logic circuitry being responsive to said last-mentioned means for energizing predetermined bars in the respective unit selected by said control logic circuitry and as determined by the corresponding character synchronously derived from said circulating register, said display cycle having a time period less than the thermal delay period of said thermochromic panel whereby all of said generated characters are displayed thereon continuously between successive display cycles.

2. A display system for use with a multi-unit thermochromic display panel, and the like, each unit of said display panel including a plurality of energizing bars for generating dilferent characters t-o be represented by such unit; said display system including: control logic circuitry for selecting the different units of the display panel; bar select logic circuitry for selecting predetermined bars in each unit selected -by said control logic circuitry; a recirculating register for storing at least one multi-character information word, each character in said multicharacter information word being in the form of a character code comprising N number of bits, circuit means coupled to said recirculating register for introducing said multi-character information rword into said recirculating register; and means coupled to said recirculating register for individually deriving the character codes of said multicharacter Word from said recirculating register and coupled to said bar select logic circuitry for causing said bar select logic circuitry to select predetermined bars in the aforesaid selected unit as determined by the corresponding character code derived from said circulating register, said last-mentioned means including a rst shift register having N stages for loading said circulating register to recirculate said multi-character word information therethrough, said rst shift register adapted to load said circulating register through its N-l stage after a first recirculation therethrough, a second shift register having N stages coupled to said bar select logic circuitry and means for loading the input stage of said second shift register through said N-l stage of said first shift register.

3. The display system defined in claim 2 in which said circuit means comprises character select logic circuitry for deriving said multi-character Word from the memory of an associated computer.

4. The display system defined in claim 2 and which includes a manually operated keyboard, register means coupled to said keyboard for receiving information therefrom; an-d in which said circuit means comprises character select logic circuitry coupled to said last named register means for deriving the inliormation therefrom.

5. The system defined in clai-m 2 and which includes timing counter means coupled to an associated computer to be synchronized therewith, and in which said circuit means comprises character select logic circuitry timed by said timing counter means for deriving the characters of said multi-character Word at predetermined times from the memory of the computer.

References Cited UNITED STATES PATENTS 3,147,469 9/1964 Buchsbaum 340-336 3,219,993 11/1965 Schwertz 340-324 3,307,156 2/1967 Durr 340-3241 3,323,241 6/1967 Blair et al 340-336 3,343,155 9/1967 Pahlavan 340-336 JOHN W. CALDWELL, Primary Examiner. A. J. KASPER, Assistant Examiner. 

